Introduced in June 1976 at the PC'76 computer conference, the SOL-20 was designed by Lee Felsenstein, who also was one of the
founders of the Community Memory Project, moderated the meetings of the Homebrew Computer
Club from 1975 until 1986, and designed the Osborne 1. Like the Atair and IMSAI machines,
the SOL-20 is an S-100 bus machine with 5 S-100 slots and used the 8080 as it's CPU. Unlike
the other S-100 machines of the period, the S-100 slots are mounted so that the cards lay
horizontally, one above the other. Also unlike the Altair and IMSAI machines, the SOL-20
included the video and I/O functions needed to use the machine, including a tape interface,
on it's mainboard, as well as provided various ROMs, called 'personality modules'. Among
the items Processor Technology sold for the SOL were additional SRAM and DRAM memory boards
and a high-capacity HELIOS disk subsystem. The HELIOS disk system proved unreliable in use
though so other disk systems from manufacturers such as North Star were popular. While some
have called 1975 the year of the Altair and 1976 as the year of the IMSAI, 1977 has been
called the year of the SOL. It was one of the first systems marketed as a complete, usable
system vice a barebones system that needed to be expanded in order to even be used. The built
in I/O and video systems in the SOL were based on S-100 bus expansion cards that Processor
Technology had previously released as upgrades for other machines. The SOL-20 was housed in
an attractive blue colored steel case with solid walnut side panels. The keyboard was
manufactured by Keytronic and carries a manufacture date of 3/78. Amazingly, there are
some parts on the keyboard that interchange with their keyboards manufactured nearly 25
years later.

Initially, there were to be three variants on the SOL produced:

SOL-20 - full fledged computer with S-100 bus

SOL-10 - meant to be used mainly as a terminal, lacked the S-100 expansion bus

SOL-PC - seperate SOL mainboard, no case or PSU

It's unclear if either the SOL-10 or SOL-PC were sold in any number. According to Mr.
Felsenstein, it is estimated that approximately 12,000 SOL-20's were produced. Initially,
both the cassette recorder for program storage and modified TV for the display were produced
by Panasonic. The SOL shipped with a small BASIC interpreter on tape, though a more capable
8k BASIC was available. There was also a newsleter, called 'SOLUS', published.

This particular machine retains it's original Panasonic TV monitor and cassette recorder.
It was orignally purchased in Santa Clara, California in early 1978 and was used to write
programs to control KENO machines. It has three memory boards installed, two 16k DRAM boards
manufactured in April 1978 and the 8k SRAM board that was bought with the machine. At the
time, each of the 16k DRAM boards listed for over $500 each.